linux-kernel - Questions on userspace cpu freq governor for linux-2.6-tip

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Date:	Sun, 5 Apr 2009 02:20:09 -0400
From:	Luke Gong <lukejgong@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Questions on userspace cpu freq governor for linux-2.6-tip

Hey,

I have compiled the latest -tip kernel (2.6.29-tip). I enabled
userspace governor for cpu freq scaling. When I am running this new
kernel with userspace governor, I found something strange. At first, I
set the cpu freq scaling governor to be userspace and set all the
cores to run at the lowest speed. But when the machine is busy, I
found the cpu speed increased and would not stay at the level set by
the userspace governor. In the kernels other than this -tip one, I
never saw this before. I am wondering if I have missed something or it
is a bug for linux -tip kernel.

Here is the snapshot:

[root@...112 ~]# cat /sys/devices/system/cpu/cpu0/
cpufreq/scaling_governor
userspace
[root@...112 ~]# echo 2000000 >
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
[root@...112 ~]# cat
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
2000000
***********************************
Then I start to run a cpu-intensive workload, now the speed increases.
***********************************
[root@...112 ~]# cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
3000000

I am using a server with 2 Xeon5450 Quad core with cpu freq from 2GHz
to 3GHz. Any comment is welcome and appreciated to be CCed to me.

Thanks.

-- 
Luke
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